You can delete or un-publish an infographic you already published by going to your account menu then "My Visualizations" and then clicking on "Published Infographics" on the left.
Unpublishing deletes the public version of your infographic but keeps it in your dashboard privately. Un-published Infographics in your dashboard are only visible to you. Deleting an infographic deletes it everywhere. Deleting cannot be undone.
Go to your account menu > then click on "My Visualizations" > click "Published Infographics" on the left > click on the infographic you want to un-publish > in the top left click on "Unpublish"
To Delete: Look for three dots under each infographic. Click on them, and you will see the option to delete. It looks like this.
If you would like to remove your previously published infographic from Google, you can use this tool.